Data compression technology is a technology that reduces transmission time or saves memory space by removing unnecessary portions when transmitting or inputting data. For example, if the document is transmitted by fax, it takes time to send space between letters and space between lines together, so transmission time is reduced by data compression by transmitting data using simplified signals of the space portion or simplifying the repeated data. When magnetic tapes or disks are used for inputting data, the technology saves the memory.
In compressing data, a technology of generating compressed data including information for identifying the type of the compression algorithm after applying a certain compression algorithm to the original data is widely used. It is common for the original data to be saved in file units, the file system storage unit of a computer system. That is, after one or more files are specified, the compression algorithm is specified for compression. It is possible to specify different compression algorithms for the specified files.
Further, in some file types, compression of data of certain portions are meaningless because they have been already compressed. Also, there are situations when optimal compression algorithms are different for different portions of one file. However, even in such a case, only one compression algorithm can be used for one file, so it is impossible to apply different algorithms for different portions inside the file.
Also, in the case of some compression algorithms, the maximum data length that can be compressed is limited, thereby making it impossible for some large-size data to be compressed. For example, in compression algorithms where the data length for compression should be less than 4 Giga bytes, it is impossible for data larger than 4 Giga bytes to be compressed.